perf script: Fix unknown feature comment

"perf script -v" emits:

unknown feature 3, continuing...
unknown feature 4, continuing...
unknown feature 5, continuing...
unknown feature 6, continuing...
unknown feature 7, continuing...
unknown feature 8, continuing...
unknown feature 9, continuing...
unknown feature 10, continuing...
unknown feature 11, continuing...
unknown feature 12, continuing...
unknown feature 13, continuing...
unknown feature 14, continuing...

These are all new features added by fbe96f29. Update
perf_file_section__process to know they are valid feature ids.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1318984464-20650-1-git-send-email-dsahern@gmail.com


Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>